The aircraft engine design process seeks to achieve the best overall system-level performance, weight, and cost for a given engine design. This is achieved by a complex process known as systems analysis (SA), where steady-state simulations are used to identify tradeoffs that should be balanced to optimize and evaluate individual technology benefits offered by the system. When applied to aviation propulsion systems, these analyses produce results that help guide technology investment, architecture, and program planning and formulation throughout the life of the program. The steady-state simulations and data on which systems analysis relies, however, may not adequately capture the true performance trade-offs that exist during transient operation.
There are a number of tools available for SA that may be used to determine the steady-state performance of a conceptual design, such as custom cycle decks, which are steady-state engine models typically developed by engine manufacturers, and the Numerical Propulsion System Simulation (NPSS). These tools can be integrated with other processes to perform a steady-state system-level optimization. During these simulations, an engine model is driven to specific power reference values, typically defined by fuel flow, thrust, or fan speed, and the engine and engine components' data are recorded for analysis. This analysis usually includes several specific flight conditions of importance, such as at takeoff and cruise. The engine components' actual transition from one operating point to another, however, is not taken into consideration by traditional systems analysis.
Aircraft engine design requires assessment and analysis of the relationship between the design constraints (e.g., high pressure compressor surge margin) and performance (e.g., time response) throughout the engine life cycle while including engine degradation information and leave room for acceptable margins. The mechanism for analyzing turbine engine dynamic capability analyzes the trade off between the design constraint and performance but typically only considers a single engine degradation. When engine degradation level is added, it is more difficult to see the true trade off. With engine degradation information added, clusters form around each design point and it is difficult to analyze worst case scenarios.